Generally, mobile device targeting and retargeting for ad purposes utilizes two different methodologies in order to identify a mobile device and provide device-specific ads: one for native applications installed on the mobile device and another for websites rendered by a browser application on the mobile device. For native applications, a software module (such as an SDK) embedded in the native application can capture a device-specific identifier (e.g., IDFA in Apple iOS™, AAID for Android™) when sharing of the device-specific identifier is enabled by the user. In order to opt-out of retargeting activity, a user can simply turn off sharing of the device-specific identifier in the settings of the mobile device, and the device is no longer retargetable.
For mobile browsers, websites can drop cookies (e.g., first-party cookies, third-party cookies) to track the user's activity in the browser for retargeting purposes. Recent developments—such as Apple's integration of Intelligent Tracking Prevention (ITP) in the most recent version of its Safari™ mobile browser—are trying to limit retargeting in mobile browsers by blocking or partitioning cookies for domains flagged as “trackers.” As a result, when serving browser-based ads, such tracking domains are unable to identify the user or mobile device and its activity history in order to deliver a user- or device-specific ad.
However, these developments also create an asymmetry between the way users can opt-out of tracking for mobile applications and in the mobile browser. As noted above, for native applications, users can switch off their device-specific identifier which will stop targeting in all native applications. No such mechanism exists for the mobile browser. As such, initiatives such as ITP may make it more difficult to implement a reliable in-browser opt-out mechanism for mobile devices.